Yeap I do the same. And found the same.

 

averaging about 25 on the PCM., so 23.5? Still twice what the expedition got.

Got 20 towing my racecar to the track, again double.

 

My best to date was 31mpg (hand calculated), which was all highway driving from Baltimore to Providence, via an overnight stop in Brooklyn. The next trip averaged 68mph and 29mpg, although it was partially in the mountains. City driving I get low 20s.

 

These numbers are very impressive ... can't wait for arrival.

 

I think the discrepancy between hand calculations and the car computer has to do with the built-in speedometer error. Corporate bean counters and lawyers cause the speedos to read ~3 mph slower than indicated. It's a liability thing. I got this number by comparing the speedo to a GPS app on my iPhone. So I'm doing an measured 57 when the speedo says 60, which translates into a 5% error. Subtracting 5% from my indicated 36.2 means my best so far has actually only been 34.4 mpg

//greg//

 

Some impressive numbers here. Since it looks like entry and drive will be available for MY '14, I really hope my wife will enjoy test driving one of these!

 

Is there a way to display overall MPG rather than for just that trip in PCM?

 

I got 12 today!! Happened to be while auto crossing, but that's worth something right

I'm guessing 12 is just the bottom of the scale because the distance to empty and my overall kept dropping significantly.

 

My speedometer shows indicated speed of 73, Garmin GPS speed 70. This is a 4% error. Overestimating the distance traveled by 4%. To get truly accurate mileage we should subtract 4% of the miles from the odometer reading in order to calculate an accurate mileage. Even when we calculate the mileage we over overestimating the MPG by 4%.

If the computer overestimates by 5% that would mean the computer overestimates by 9% over actual.

Something to think about.

 

Any mods to help MPG?

on a Subaru STi, a 2 inch lip on the front air dam increases highway mileage by 2mpg.

Are there any front air dam's available for the CD, maybe something in the Porsche family?

 

Speed and distance traveled are two different things though - just because the car thinks you got there faster does not mean that the distance is further. In other words, the speed and distance are not tied...unless I'm missing something here.

 

let me see:

MPH is distance per hour

If the speed is higher per a given time it means more distance was traveled.

The only except would be if there was a separate cable, ie mechanical measurement for the odometer.

 

True, however total distance traveled is not linked to speed. If you drove 90mph instead, that doesn't increase the trip's total miles.

Your odometer is correct, it's the speedo that's off.

 

This is an old thing and there is lots of information out there about it. Speedos can have a lot of slop in them and will even vary between cars built on the same day. I've seen speedos up to 10% off.

And no the mfg is not likely to do anything about it unless it under reports. It's the laws about it under reporting that have them err on the over reporting side.

Your ODO on the other hand has some strict regulations about how accurate it has to be and a "bad" one will only be off by a mile or two every 5-10k. If you find that your ODO is under or over reporting, you get that documented and addressed ASAP.